Evolution of the Earth David Spergel. Evolution of Earth’s Atmosphere Earth lost its early atmosphere in major collisions (first 10-100 Myr) Subsequent.

Evolution of the EarthEvolution of the Earth

David SpergelDavid Spergel

Evolution of Earth’s Evolution of Earth’s AtmosphereAtmosphere

Earth lost its early Earth lost its early atmosphere in major atmosphere in major collisions (first 10-100 collisions (first 10-100 Myr)Myr)

Subsequent infall of Subsequent infall of comets brought in comets brought in material from outer solar material from outer solar system and replenished system and replenished NN22, H, H220. 0.

Volcanic source of COVolcanic source of CO22

3.8 Gyr ago: 10 bar of 3.8 Gyr ago: 10 bar of COCO2 2 85 C85 C

Volcanic OutgassingVolcanic Outgassing

Volcanic gases:Volcanic gases: 95% H95% H2200

1-2% CO1-2% CO22

1-2% SO1-2% SO22

0.1% H0.1% H22SS

Losing Our AirLosing Our Air

Catastrophic Atmospheric Catastrophic Atmospheric LossLoss

Thermal EscapeThermal Escape Velocity depends on mass of Velocity depends on mass of

moleculemolecule Predicts that all light Predicts that all light

elements are lostelements are lost Does not fit abundanceDoes not fit abundance

Driven WindDriven Wind Solar EUV radiations hits H Solar EUV radiations hits H

which drives wind.which drives wind. Wind preferentially removes Wind preferentially removes

light elements that are no light elements that are no embedded in heavy embedded in heavy moleculesmolecules

Thermal distribution

OxygenOxygen

During pre-Cambrian period (90% During pre-Cambrian period (90% of age of Earth), Oxygen levels of age of Earth), Oxygen levels were > 2% of current levelswere > 2% of current levels

Biogenic production of OxygenBiogenic production of Oxygen Oxygen is highly reactive. In the Oxygen is highly reactive. In the

absence of biogenic production, would absence of biogenic production, would disappear. Free oxygen appears disappear. Free oxygen appears about 2 Gyr ago (first pollution crisis)about 2 Gyr ago (first pollution crisis)

Fe abundances in rock traces Oxygen Fe abundances in rock traces Oxygen abundances. Iron dropout of water at abundances. Iron dropout of water at the great oxygenization eventthe great oxygenization event

Appearance of ozone in troposphere Appearance of ozone in troposphere allows burst of marine productivity. allows burst of marine productivity. Increases rate of carbon fixing in Increases rate of carbon fixing in carbonates carbonates

cynobacteria

Pre-Cambrian Banded Iron Formations

a = albedo

Energy BalanceEnergy Balance

Energy In/ (from Sun) = Energy In/ (from Sun) = Energy Emitted by Energy Emitted by EarthEarth

Earth Surface

L/4D2 aL/4D2

reflected

(1-a)L/4D2

thermal

Greenhouse GasesGreenhouse Gases

Were Terrestial Planets Once Were Terrestial Planets Once Similar?Similar?

Earth, Mars, Venus have Earth, Mars, Venus have similar masses and similar masses and compositioncomposition

Carbon cycleCarbon cycle On Earth, COOn Earth, CO22 in oceans in oceans

settle into rockssettle into rocks Venus is too hot for Venus is too hot for

oceans. Water lost during oceans. Water lost during early very hot phaseearly very hot phase

Mars: No plate tectonics-- Mars: No plate tectonics-- no source for COno source for CO22

Mars: Too ColdMars: Too Cold

Early Mars was Early Mars was warmerwarmer COCO22 now incorporated now incorporated

in carbonate rocksin carbonate rocks

Evidence of running Evidence of running waterwater

Has Mars had recent Has Mars had recent episodes of high episodes of high pressure and liquid pressure and liquid waterwater

Dry lake beds on Mars?

Mars & WaterMars & Water

Evidence of running Evidence of running water on Marswater on Mars

Is there still running Is there still running water?water?

Is there life?Is there life? Focus of upcoming Focus of upcoming

NASA missionsNASA missions Are we Martians?Are we Martians?

Venus: Too HotVenus: Too Hot

Nearly Earthlike: almost the same mass Nearly Earthlike: almost the same mass and heated at similar ratesand heated at similar rates

Surface temperature ~700 KSurface temperature ~700 K Runaway greenhouse effectRunaway greenhouse effect How was Venus’ water lost?How was Venus’ water lost?

Blowoff of H?Blowoff of H? Early super-greenhouseEarly super-greenhouse

Earth: Just Earth: Just Right?Right?

Sun’s temperature is Sun’s temperature is slowly increasing. slowly increasing. Luminosity was 30% Luminosity was 30% lower in pastlower in past

Earth’s temperature has Earth’s temperature has been remarkably constantbeen remarkably constant

Higher concentration of Higher concentration of greenhouse gasesgreenhouse gases

COCO22 trapped in trapped in

carbonates todaycarbonates today

Snowball EarthSnowball Earth

Snow/ice instabilitySnow/ice instability Albedo of ice = 0.8Albedo of ice = 0.8 Albedo of sea water=0.1Albedo of sea water=0.1

Over past several million Over past several million years, multiple glaciations. years, multiple glaciations. Last one ended only 10,000 Last one ended only 10,000 years agoyears ago

About 1 Gyr ago, About 1 Gyr ago, continents were all near continents were all near equator. Ice near equator. Ice near completely covered Earthcompletely covered Earth Ice without end?Ice without end? Seems to persist for millions Seems to persist for millions

of yearsof years

Multiple EquilibriumMultiple Equilibrium

Snowball Earth IISnowball Earth II

Volcano outgassing Volcano outgassing increases COincreases CO22 to 300x to 300x current levelscurrent levels Limited plant life -> no COLimited plant life -> no CO22

sinksink Signature seen in Signature seen in 1313C/C/1212C ratioC ratio

Earth’s temperature increases Earth’s temperature increases to 50 Cto 50 C Cap carbonatesCap carbonates

Multiple cycles?Multiple cycles? Survival of life near volcanic Survival of life near volcanic

vents? Unfrozen regions of vents? Unfrozen regions of ocean?ocean?

Extinctions lead to emergence of Extinctions lead to emergence of multicellular life?multicellular life?

21st Century Greenhouse 21st Century Greenhouse ExperimentExperiment

Burning fossil fuels: we’ve Burning fossil fuels: we’ve seen that COseen that CO22 plays plays important role in thermal important role in thermal balancebalance

Global effectsGlobal effects Ice caps meltingIce caps melting Flooding of coastal regionsFlooding of coastal regions Destruction of habitatsDestruction of habitats 2 -10 K mean warming of 2 -10 K mean warming of

Earth’s surfaceEarth’s surface

Comparable to major Comparable to major climatic eventsclimatic events

IGPP report

K-T Mass ExtinctionK-T Mass Extinction Bombardment continues to Bombardment continues to

todaytoday Comet hits Yucatan Comet hits Yucatan

penisula 65 million years penisula 65 million years agoago Collision kicks up dust layer Collision kicks up dust layer

that covers Earth’s surfacethat covers Earth’s surface Nuclear winterNuclear winter Sudden disappearance of Sudden disappearance of

much of life on planet much of life on planet (including dinosaurs)(including dinosaurs)

Iridium layerIridium layer Evidence of global firesEvidence of global fires Nuclear winterNuclear winter

Deccan Traps: Dinosaur Deccan Traps: Dinosaur Killers?Killers?

Formed 60-68 Myr Formed 60-68 Myr agoago

Covered ½ area of Covered ½ area of India to a depth of India to a depth of 2 km.2 km.

Linked to Reunion Linked to Reunion Hot SpotHot Spot

Permian Mass ExtinctionPermian Mass Extinction

250 Myr ago250 Myr ago 96% of all marine 96% of all marine

species and 70% of species and 70% of all terrestrial all terrestrial vertebrate species vertebrate species become extinct. Even become extinct. Even insectsinsects

Flood Basalts? Comet Flood Basalts? Comet impacts? Methane impacts? Methane release?release?

Another Thing to Worry Another Thing to Worry About…About…

Tunguska impactTunguska impact Evidence for episodic Evidence for episodic

extinctionsextinctions Proposals for large scale Proposals for large scale

astronomical surveysastronomical surveys Bad Hollywood moviesBad Hollywood movies Role of Jupiter as Role of Jupiter as

Planetary ProtectorPlanetary Protector